Name: UNDERSTANDING GENOTYPE AND PHENOTYPE
Activity: Students will get a bag of shells from two beaches, sort them, identify them and look at variations.
Level: 3
Developer: Alberto Mimo
Site: Classroom or Laboratory with access to a computer and excel.
Subjects: Genetics, statistical analyses.
Introduction
Darwin and Russell in the 1800’s were interested in understanding how new species came about. They concluded that somehow random changes in their phenotype were best adapted to an environment or situation and those organisms that did not fit would die out, or lived at a disadvantage because they were not well fitted to the new condition. This is in essence the idea of evolution based on natural selection due to the survival of the best-fitted animal or plant. At the same time, a man named Jean-Baptiste Lamarck theorized that animals evolved by the force of adapting themselves to a new environment and changing their phenotype. Long-neck giraffes get longer necks by trying to reach the leaves on the taller trees. In this lesson, we explore the idea of phenotypic plasticity based on environmental conditions or contact with other species
A living organism’s DNA contains the information that will be transferred to its progeny. Some information is not shown physically or physiologically, but it is all there in their genome. Some of the information is displayed in every organism either in its shape or form or in its physiology. (Read about Gregor Mender, 1822-1884) One is called the organism’s genotype and the other is the organism's phenotype.
Organisms within a species are not always exactly alike, there is a variation within each species that refers back to the exact genome they have. In people, some kids have blue eyes and some dark brown, but this variability has to be all accounted for unless there has been a mutation. Mutation could lead to new species, but that is only when that mutation shows to provide that organism with an advantage. See Darwin and Russel's theory of Evolution.
Variability within one species could have been led by small changes in the habitat, other species' competition, or a predator/ prey relationship. (Anurag A. Agrawal in his paper “Phenotypic Plasticity in the Interactions and Evolution of Species”) Published by the Journal of Ecology in 2001 shows how these changes can be derived from competition, mutualism, predation risk, and parasitism/herbivore or food quality.
Thomas J. DeWitt, Andrew Sih, and David Sloan Wilson in their paper “Cost and limits of phenotypic plasticity” Trends in Ecology & Evolution, 1998, discuss the idea that variations on an organism's phenotype have limits and cost. Some of this cost includes Maintenance and Production of the Phenotypic Change, Information Acquisition Cost, Development Instability, and Genetic Cost, but at the same time, there is a benefit of survival.
Some of the terminologies associated with phenotypic plasticity are: (Phenotypic Plasticity and the origin of diversity. Mary Jane West-Eberhand, Annu. Rev. Ecol. Sust. 1989 20:249-78).
- Alternative phenotypes: Two or more forms of behavior, physiological response, or structure maintained in the same life stage in a single population and not simultaneously expressed in the individual.
- Conditional (or condition – sensitivity): The alternative adopted by a particular individual or at a particular time depends on environmental conditions.
- Allelic-Switch: The alternative adopted by a particular individual depends on the allele(s) present at one or more genetic switch loci.
- Combine switch: The alternative adopted depends on a combination of allelic and environmental factors.
- Polyphenism: The existence of environmental-cued alternative phenotypes in a population.
- Polymorphism: The existence of morphological district alternatives in a population (usually: “allelic-switch alternatives”.
Hypothesis
Slipper Shells live at the bottom of the Long Island Sound. They form a tight community of shells at the bottom of the seawater and are constantly subject to being swept away by the current caused by the incoming and outgoing tides. In areas with narrow channels the effort by the shells to stay in place is greater and in more level areas where the current is less strong the effort of the shells is also less. The speed of the water at different locations within the Sound changes depending on the site, for example, areas located at the entrance of the sound called the race have stronger currents.
The hypothesis here is that at locations where the speed of the water current is high; shells will transform their shape to be more flat reducing the friction with the water. Shells that live in more tranquil areas will be shaped more bumped or higher in the top. So we have two possible different phenotype shapes on these shells. The idea here is to take measurements and see if we can find differences within collection sites. Have C. fornicata shells a phenotypic plasticity?
Read Phenotypic Plasticity and the Origen Of Diversity. Mary Jane West-Eberhard. Annu. Rev. Ecol . Syst. 1989. 20:249-78
Natural History and Anatomy of the Slipper Shell (Crepidula fornicata L.)
Slipper Shells live out in the bottom of the Long Island Sound. They are found in amazing quantities and compete for habitat with oysters and other organisms. These mollusks stack one on top of the other forming a thick layer. During reproduction, they form clusters where the ones at the bottom are females and the ones on top are males. The eggs are found in sacks that are fertilized in the water and released. These organisms are hermaphroditic, so they change sex as they grow. Starting as males and growing into a female, they live for about 7 to 10 years. You can count the number of growth rings. When they die they are carried away by the tide and the water current. They have very few predators so they are a nightmare to the oyster industry.
A cluster of Slipper Shells from the bottom of the LIS (Long Island Sound) mixed with mud from the site. These shells were collected using a drudge from a science vessel. (Next 3 pictures)
Mud and shells covers the see floor
Some are on top of other; the lower one is a female